The present invention relates to hook and loop fasteners.
Hook and loop fasteners comprise mating strips or patches of filamentary stress-bearing hooks and loops. Monofilament or multifilament loops are knit or woven into a textile backing, or ground, to form the loop component of the fastener. To form the hook component, monofilament loops are woven in the same manner, then passed through a hook cutting process in which portions of the monofilament loops are cut away to form hooks. The loops and hooks will be referred to collectively herein as "pile".
A binder is applied to the ground side of the hook or loop component, in a manner so that it impregnates the ground, in order to supplement, with an adhesive bond, the frictional interlocking of the pile filaments with the ground filaments that results from the weaving process.
The binder matrix adds strength and durability to the fastener. Depending upon the quality of the binder, the hooks and loops may pull out of the ground, and the ground may start to fray, after a number of cycles of closing and opening the fastener. Damage may also occur during manufacture of the fastener, e.g., to the loops during a "napping" process in which they are contacted with a roll having a surface formed by cut wires in order to extend the loops and thus increase the peel strength of the hook/loop bond, or to the hooks during the hook cutting step described above.
Thus, the strength of the binder is important in providing sufficient resistance to hook or loop pull out during manufacture and use. The material used for the binder will greatly affect the fastener's performance. It is desirable that the material be able to withstand numerous cycles of opening and closing, and not break down appreciably under laundering or dry cleaning conditions.
In addition to the particular material used for the binder, the manner in which the binder is applied can affect the fastener's performance. For optimal strength, the binder should impregnate the ground as fully as possible. At the same time, it should not be allowed to wick into the hooks or loops, as that interferes with their ability to engage each other and reduces the effectiveness of the fastener.
The manner in which a binder is applied also affects the cost to produce the fastener. Current fasteners often use binders which are applied to the ground as a solution or as a dispersion. These binders require additional chemicals to effect their cure (cross-linking), and ovens to dry them and promote cross-linking; the production line can be quite long as a result. The chemicals used to cross-link the binder, e.g., formaldehyde or aziridines, are often environmentally undesirable, if not toxic. Other, hot-melt binders require that the ground and binder be heated during application. Thus, high energy and capital costs, extensive factory manpower and floorspace, and environmental undesirability are often associated with the binders currently used in hook and loop fastener systems.
New binders are continually sought which would be low in cost, easy to apply at high production rates, and which, in use, would be highly resistant to the conditions encountered by hook and loop fasteners, e.g., laundering and dry-cleaning.